It's fair for international public health leaders to take pride in the vastly improved rates of child immunization around the globe over the past three decades. But a new report from the U.S. Centers for Disease Control reveals key areas where more effort is needed.

The data, from 2011, show that the majority of unvaccinated children are in India, Nigeria and Indonesia. Those three nations account for more than half of the 22.4 million children who had not received three doses of the diphtheria-tetanus-pertussis vaccine during the first year of life.

The statistics reveal substantial progress in minimizing the number of unvaccinated children since the 1974 founding of the global Expanded Program on Immunization. However, 20 percent of the world's children, clustered in low-income countries, are not fully vaccinated during the first year of life with the four traditional vaccines against polio, tuberculosis, DTP and measles.

Worldwide, vaccination for tuberculosis was 88 percent, while 83 percent of children received their third dose of polio vaccine. DTP vaccination is more problematic and suggests that public health officials in some countries may need to rethink their vaccine delivery systems.

The number of children receiving a third DTP dose in 2011 was similar to the rate in 2009, the authors noted. More than eight million children worldwide got a single DTP dose but dropped out before completing the three-dose series.

Attitudes favoring vaccination are growing stronger in developing countries, but distribution system glitches may be the reason for more unvaccinated children.

"Strategies to improve vaccination coverage might differ for those children who have never been vaccinated, compared with those who have started but not completed the immunization series," said the authors of the report, led by Dr. Samir V. Sodha of the CDC's Center for Global Health.

"Children not completing a three-dose series of vaccines, such as the series for DTP vaccine, indicates that there is a problem with the services being delivered," Dr. Orin Levine, director of vaccine delivery at the Bill & Melinda Gates Foundation, told Take Part. The Gates Foundation has made global child immunization one of its top priorities. "This poor utilization of immunization services can be a result of a number of reasons, including long wait times, lack of service availability (vaccine stock outs, health workers not present), lack of funds for transport to the clinic, unclear follow-up instructions after initial immunization visit and negative experience by the parent."

Global immunization strategies have focused on four vaccines, but several newer vaccines are being added, an effort that holds great promise for improved child health but one that may further tax immunization systems in developing countries. By the end of last year, 180 countries had added hepatitis B vaccine in into their programs, and 94 of those countries recommended a first dose of hepatitis B within 24 hours of birth to guard against perinatal transmission.

Worldwide, 75 percent of children received all three doses of hepatitis B, including those countries not using the vaccine at all.

Another newer vaccine, Haemophilus influenzae type b vaccine, has not reached the levels of worldwide use seen with the hepatitis B shots. Only 3 percent of children got their third shot of of Haemophilus influenzae type b vaccine.

Rotavirus vaccine has now been introduced in 31 countries—16 percent of those surveyed. Only 9 percent of children worldwide received the complete rotavirus vaccination series last year. Pneumococcal conjugate vaccine is offered in 39 percent of countries, with 12 percent of children worldwide receiving three doses.

But the greatest effort will remain focused on the three nations with the most unvaccinated children—India, Nigeria and Indonesia. Public health leaders have stepped up their efforts to reach pockets of the world most in need of stronger immunization services. World Health Organization members endorsed a global vaccine action plan in May to improve rates.

"This disproportionate burden presents a significant challenge and each country will require solutions tailored for their unique contexts," Levine says. "There is reason for optimism, however. In India, the country is nearly two years out from the last confirmed case of polio. While the government and partners remain vigilant in preventing a backslide, the reprieve has allowed greater focus on addressing other vaccine-preventable diseases, through efforts to bolster the routine immunization program."

Question: Do you think an international public health effort can significantly reduce the number of unvaccinated children? Tell us what you think in the comments section.

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